add basic aliases to work with tmux
add helper function to install completion
install completion for tmux if needed
system copypaste mode for vim inside tmux

Use unnamed register on Vim allow to use system clipboard, but if Vim working
inside tmux session on mac this require one more extra step:

$ brew install reattach-to-user-namespace

That's all, now your Vim works wonderfully in tmux.

See http://robots.thoughtbot.com/post/19398560514/how-to-copy-and-paste-with-tmux-on-mac-os-x
for more details.
more useful git aliases

* `gl` ~ `git log`
* `gpl` ~ `git pull` (compare `gp` mean `git push`)
add custom autogroup for lua language

Expand tab to 3 spaces and short lines (easy to read in small terminal window).
small cleanup

* Remove unused font declaration
* Remove unpaired end foldmarker
change default guifont to Ubuntu Mono pathed for Powerline
add bindings to make markdown headers
use skeleton template for new files

* Does not need to specify `autocmd` for each filetype, use extension to detect
  skeleton filename
* Remove trailing blank line
keep undo works between Vim sessions
add path to less compiler to $PATH
enable color output for grep